Heaven and Hell in dbz are not the size of UniverseActually i have reason to believe Afterlife (Spiritual Universe) is larger than the Physical Universe. But this doesnt matter.
Manga Author already created an Image of the DB Universe and Physical & Spiritual Universe are the same size in DB verse.
Kaioshin Holy Sphere is located outside the Universe, which is why it was a big deal that Goku got there and Goku power is sensed there.
Kaioshin Sphere orbits the Universe like a satelite.